Hornworts

Domain Eukarya

Kingdom Plantae

Phylum Bryophyta

Anthoceros: gametophyte thallus with elongating sporophyte

Why is this called a “hornwort?”

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http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Anthoceros.jpg

Gametophyte

Anthoceros - the hornwort

The gametophyte is much like a thallose liverwort.The sporophyte is the horn of the hornwort.

Hornwort Thallus Cross Section photosynthetic upper epidermis

cortex

lower epidermis

rhizoids

Compared to the liverwort thallus, what is missing?

Cyanobacteria are often symbionts!

What cellular details can you find?

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http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Pyrenoids_MC.low.jpg

The Anthoceros gametophyte thallus has one chloroplast per cell...

Obviously like all other bryophtyes:chlorophylls a and bxanthophylls and carotenoids

Compared to the liverwort, what is different about the location of the antheridia in hornworts?

Antheridium sterile jacket

Spermatogenic tissue

Stalk

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http://www.dipbot.unict.it/sistematica_es/Immagini/18002.JPG

This Anthoceros gametophyte…

Antheridium sterile jacket

Spermatogenic tissue

Lower Epidermis

Rhizoids

Thallus parenchyma

Upper Epidermis

shows three antheridia…

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Here is the best I could find on the web to show the archegonium which is embedded in the hornwort gametophyte thallus.

Apical Cell

Sterile Jacket Cells

Neck Canal Cells

Ventral Canal Cell

Egg Cell

The artist would lose one point above…why?What are some missing items as well?

The “spore mother cell” is better known as sporocyte!

We shall find out why this is so, as we proceed to more-derived plants.

sporangium

stalk

footintercalary meristem

gametophyte “collar”

Hornwort sporophyte (with attached gametophyte)

Whole mount closeup

What apomorphy is featured here?

Longitudinal section

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http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Sporophyte_foot_MC.jpg

The Anthoceros sporophyte foot is embedded in the gametophyte.

The sporophyte seta has an intercalary meristem.

Foot

IntercalaryMeristem

GametophyteThallus

Gametophyte rhizoids

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http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/stomata.jpg

The Anthoceros sporophyte has evolved guard cells and stomata.While initially dependent on the gametophyte, it carries out its own photosynthesis.The sporophyte may continue to grow while the gametophyte degenerates.

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http://www.personal.psu.edu/faculty/t/r/trp2/anthoceros.jpeg

Two apo-morphies are shown here… which?

What is this?

How could it be labeled?

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http://www.puc.edu/Faculty/Gilbert_Muth/phot0123.jpg

sterile jacket

sporocyte

The Anthoceros sporangium is linear and indeterminate in size.It is surrounded by a layer of cortex and epidermis.

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http://www.biology.lsa.umich.edu/courses/bio255/antho2.jpg

The sporocytes divide by meiosis, producing meiospores.The tri-radiate marks and surfaces that the tetrad of spores impress upon each other are shown here.

Hornwort sporangium ls

cs, ls, or wm?

What would be the labels on this?

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http://www.biology.lsa.umich.edu/courses/bio255/antho.jpg

The sporophyte shows a cutinized epidermis, a step up

from the gametophyte.

Spores appear in tetrads (the four meiotic products) of which three are generally in any plane of section

In the center of the sporophyte, you can find the hydroids and leptoids!

The cortex cells are responsible for the photosynthetic support for the sporophyte.

Here is the cross section of a maturing part of the “horn”…the Anthoceros sporophyte.

The sporophyte maturing to shed spores to the wind

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http://botit.botany.wisc.edu/images/130/Bryophytes/Anthocerophyta/Sporophytes_lg_DH_.jpg

The Anthoceros sporophyte matures from tip to base shedding almost unlimited spores due to intercalary meristem at base.

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http://www.hiddenforest.co.nz/bryophytes/hornworts/anthocertaceae/images/horn03.jpg

The tip of the Anthoceros sporophyte matures first, shedding the spores to the wind.

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SYNGAMY

zygote

SporophyteGametophyte

sporangium

sporocytespores

gametangia

gametesgermination

mitosis

differentiation

mitosisgerminationmitosis

mitosis

1N 2N

differentiation

differentiation

differentiation

MEIOSIS

The Life Cycle of Anthoceros